Baltz, who is with the Oasis Day Spa in Manhattan, experienced an immediate connection with the stones. After taking his first LaStone workshop in 1998, Baltz started reading about Native American spirituality. "Most indigenous people have worked with stones," says Baltz, who developed the deep-tissue workshop for LaStone. "I believe the stones have their own energy. I believe they have a lot to teach us."

Many therapists collect their own stones. Some come from riverbeds; others are formed from white marble. Hannigan uses 54 hot stones, 18 frozen stones and one at room temperature in each massage. LaStone sells stones, but only to therapists who are registered to take a training workshop.

At Spa du Monde in Washington, where Hurt works, the stones are kept in the front window where they are warmed by the sun. Prior to a massage, they are heated further in hot water. LaStone therapy is available in almost all 50 states, including Alaska and Hawaii, said a LaStone spokesperson. Trained LaStone therapists also offer massages in Puerto Rico, the Virgin Islands, Austria, England, Germany, Italy, Japan, Mexico and Spain. Treatments last from an hour to an hour and a half, and prices range from $60 to $180 depending on the extent of the massage.

According to Hannigan, many of her clients are in a deep meditative state by the end of a session. "My life is very different now, not just professionally but personally too," says Baltz. "In our culture, we tend to think of life as linear, that everything has a beginning and an end. Now I see that my spiritual life and my work are a circle."